16 The Development of the Lungs 
bit, and guinea-pig, he describes the growth of the tree after the forma- 
tion of the primitive lung sacs as taking place by monopodial growth 
with acropetal development of lateral twigs. In this process the stem 
bud is the principal structure, which grows on undivided with the ventral 
bronchi originating as lateral outgrowths upon it. The primitive lung 
sacs are to be looked upon, according to Narath, as the first stem buds. 
By this process arise from the stem bronchus two series of lateral 
branches, the ventral and dorsal bronchi. While the former are true 
derivatives of the stem bronchus, the latter, Narath is inclined to 
regard, as branches of the ventral bronchi which in course of ontogenetic 
and phylogenetic development are given up to the stem bronchus. From 
his embryological investigations, Narath supports Aeby’s conclusions 
with reference to the dorsal and ventral accessory bronchi. They are 
formed first on the ventral and dorsal branches and then wander to their 
positions on the inner and ventral side of the stem bronchus. In this 
group and in complete accord with Aeby, he would also classify the 
Bronchus cardiacus except that, unlike Aeby, he believes it can arise in 
some instances from the second or third ventral bronchus. The pulmon- 
ary artery according to Narath’s view has no great influence on the growth 
of the bronchial tree as he, like Zumstein, has found a whole series of 
variations in the artery without any important changes in the bronchi. 
Furthermore, he reiterates Zumstein’s view that, both at the time the 
primary bronchi are formed, as well as later, the pulmonary arteries are 
thin, weak vessels of insufficient strength to influence these relatively 
thick and well-developed epithelial structures. Of equal importance in 
this connection is the observation that the arteries cross over the bronchi 
to pass down on its lateral, instead of its dorsal, side. Only at the end 
of the stem bronchus is its position distinctly dorsal. In consequence 
of this course, it forms a half spiral round the stem bronchus. Of a 
crossing in the sense of Aeby no true case exists. Narath accordingly 
proposes to abandon the distinction between the so-called eparterial and 
hyparterial regions of the bronchial tree. 
The eparterial bronchus of Aeby has, according to Narath, the same 
area of distribution as a dorsal bronchus. He not only regards it such, 
but believes it is in reality, the first dorsal bronchus. ‘To emphasize its 
special meaning for the topography of the lung, he terms it the apical 
bronchus. It is never suppressed nor does it degenerate in certain ani- 
mals as Aeby suggests. It is, furthermore, always present normally as 
a lateral branch of the first ventral bronchus and possesses, moreover, 
the power of wandering up either onto the stem bronchus or the trachea. 
In speaking of his conviction that it is a real dorsal bronchus he con- 
